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Notesare reconverted in the hot acetic anhydride. The solid complexes appear quite resistant to hydrolysis so that no special precautions during handling are necessary. All spectra were determined on a Cary 14 spectrophotometer, maintained at 25 ± Io, using cells of 1-cm or 10-cm path lengths. Absorption maxima for a few cases, as indicated in Table I, were determined with an equivalent concentration of donor in the reference cell to compensate for partial overlap from neighboring absorption bands. The formation constants and molar absorptivities were calculated by means of the Benesi-Hildebrand equation. Where there was interference from neighboring bands, as indicated in Table II, calculations were carried out on data obtained from the long-wavelength sides of the absorption bands.7 Results and DiscussionThe maxima of the charge-transfer spectra for the PMDA-aromatic hydrocarbon complexes in six solvents are listed in Table I. Despite an apparent general trend, benzene solutions excepted, of the charge-transfer maxima toward shorter wavelengths

New organic resin systems are in constant demand because of the increasing use of fiber-reinforced organic matrix composites to replace metallic components in weight-critical aerospace and advanced marine applications. High temperature capability, low moisture absorption, and improved storage and processing properties are emphasized for new composite matrix materials. Diether-linked phthalonitrile resins recently developed at NRL promise to meet these requirements and are being evaluated as potential candidates for such applications. The linking structure R in the monomers include bisphenol-A, bisphenol-S, bisphenol-A6F, resorcinol, hydroquinone and dihydroxybiphenol. The results of the characterization of cured phthalonitrile resins are presented. This includes their thermal properties from thermal gravimetric analysis and differential scanning calorimetry, spectroscopic properties from the infra-red and nuclear magnetic resonance techniques, and mechanical properties from torsional pendulum analysis and fracture mechanics evaluation. Compared to conventional metallic structural materials, fiber-reinforced organic matrix composites have a very high specific modulus and tensile strength. For this reason, they are being used in many aerospace and marine systems in which weight reduction is an important consideration. This reduction is especially critical for the successful development of new vertical and short take-off and landing (V/STOL) aircraft in order to compensate for the large engines required for vertical lift.Composite materials have been used successfully, and conventional matrix materials such as epoxies are being considered for application in V/STOL systems. Epoxy polymers, however, suffer many shortcomings. They are extremely sensitive to moisture absorption, which causes a large reduction in their glass This chapter not subject to U.S.

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